AIS (Universal Shipborne Automatic Identification System) is a system constructed to easily grasp existence of one or more perimeter ships around a ship concerned and traveling statuses thereof.
Conventionally, ships that satisfy a predetermined condition are required to equip a device that can transmit AIS information (AIS transceiver) thereon. The device wirelessly transmits, to the perimeter of the ship concerned, positional information and traveling information of the ship concerned (hereinafter, may simply be referred to as “the ship”) at a predetermined cycle according to the traveling state of the ship (e.g., moored or moving), by using a frequency within a VHF band. The AIS information is received by the one or more perimeter ships or a land station, and thereby, information on the ship can be acquired (e.g., ship position and speed).
Meanwhile, JP2005-141656A discloses such an AIS transceiver, and points out the possibility that information which is different from the face may be transmitted to a receiver side intentionally. In JP2005-141656A, in order to solve this problem, the application of an authentic method using a public key cryptosystem as a transmitter securing means which is mathematically difficult to alter is proposed to prevent misconduct of an operator of the ship, such as faking the AIS information.
However, in an actual situation of ship operation, other than such an intentional misconduct by the operator, even when there is no such intention, there have been cases where the AIS information including wrong contents is transmitted due to, for example, defects of the sensors or a misinput of information by the operator. Such unintentional mistake cannot be solved even by the method in JP2005-141656A, and for smooth ship travel, a means for easily confirming information to be transmitted to other ships on the ship side has been desired.